None of the stations is in the Washington area, but the change could potentially confuse television viewers elsewhere who were expecting to have four more months to make the transition to digital TV, as was approved by Congress this month.

Although Congress voted to delay the nationwide transition to June 12, the bill allowed stations to make the switch early with the approval of the Federal Communications Commission. The agency said it wanted to reserve the right to prevent stations from switching earlier if doing so posed a threat to public safety in particular markets.

Last week, nearly 500 television stations told the FCC that they intended to change to digital broadcasts at midnight tonight, the deadline for the switch they had been planning on for three years. The FCC initially responded that 123 stations could not switch early, largely because in some markets every major commercial station was planning on doing so, and that could have left some consumers who do not yet have digital-enabled TVs without access to important public safety information and news alerts. The FCC later amended that number to 106.

Stations that still want to turn off analog signals can do so if they take steps to mitigate the effect and make sure viewers are aware of the switch, the FCC said. For example, stations would have to make sure that at least one analog signal is still on the air in their market, keep some sort of analog signal on air for 30 days after the switch, and step up their efforts to inform the public about the change. Fifty-three stations said they would take such action and switch early, 10 are in limbo pending hardship appeals, and 43 said they would wait until June.

All told, about one-third of the nation's TV stations plan to switch by the original deadline tonight.

Washington area stations have said they plan to keep analog signals on the air through June.

The major broadcast networks, including ABC, CBS, Fox, and NBC/Telemundo, agreed that the stations they own and operate would continue to broadcast in analog until June but that affiliate stations could choose when to switch. The FCC has sent employees to 72 markets where one or more of the top four network affiliates are dropping analog broadcasts.

Some stations said they decided to keep analog signals on the air for public safety. Pat Baldwin, president and general manager of the ABC affiliate in Tulsa, said the station initially planned to go all-digital early but last week decided to wait after a tornado touched down in the station's coverage area. The station reaches rural viewers who may not otherwise have access to severe weather warnings, he said.

Two hundred stations, including stations in Wilmington, N.C.; Hawaii; and Chico-Redding, Calif., have already made the transition to all-digital TV.

Viewers in markets where stations are going ahead with the switch who are having trouble receiving digital broadcasts can call the FCC's help line at 1-888-CALL-FCC.